Sprint today announced the availability of its 4G LTE network to customers in 21 more markets, including Los Angeles, Contra Costa County, Calif., Charlotte, N.C., Norfolk, Va., and Memphis, Tenn. And now through May 9th, customers switching their number to Sprint from another carrier can save up to $100 on any smartphone with a new two-year service agreement and qualifying plan. Here's more info:

Sprint continues to bring a better wireless experience to more customers across the country as it builds out its all-new 3G and 4G LTE network. Many Sprint customers are discovering Sprint 4G LTE in cities that haven't yet officially been announced, including Washington, D.C., New York and San Francisco. Sprint has announced more than 170 markets where LTE will be available in the coming months, and is adding the following markets to that list today:

Sprint offers a wide range of 4G LTE devices, including the Sprint Force, Samsung Galaxy Note II and Kyocera Torque. Sprint expects to continue its smartphone success throughout 2013 with the launch of HTC One on April 19, Samsung Galaxy S 4 in the second quarter, and the BlackBerry Q10 smartphone later this year. Sprint offers these devices with its improving 3G and 4G LTE network experience and Sprint's Everything Data plans - including Any Mobile, Anytime, unlimited Web, texting and calling.